At a glance, the skulls of Dimetrodon look quite similar. Their main difference is in size. But the teeth of Dimetrodon are a different story. Details in enamel and dentine, Brink and Reisz report, distinguish three different kinds of cutting edges that distinguish smooth-toothed biters from those capable of a saw-edged chomp.

The oldest and smallest species in the study, Dimetrodon milleri, had teeth with straight cutting edges. Sharp, sure, but not especially well-suited to cutting through skin and muscle. By the time of the later, larger Dimetrodon limbatus, though, these carnivores had evolved small serrations in the enamel along the cutting edges of some of the teeth. The teeth of Dimetrodon grandis were even more specialized for cutting. Teeth in